DESCRIPTION (provided by investigator): The establishment of boundaries between cells and tissues is a critical feature of pattern forma- tion in every animal embryo. These same boundaries must be maintained and new ones established as organogenesis and growth continue during later post-embryonic development. Still later in the adult, the maintenance of cell and tissue boundaries is essential for normal homeo- stasis. The mechanisms underlying such boundaries are thus of fundamental biological significance. Yet these same mechanisms also have profound implications for a variety of genetic diseases, cancers, in which boundary constraints are lost, and regenerative contexts, in which boundaries must be formed anew. The goal of this project is to understand the genetic and cellular mechanisms underlying cellular boundaries in post-embryonic vertebrate development. To this end, these studies will employ an especially tractable example of boundary formation, the development and maintenance of adult pigment stripes in the zebrafish. Previous efforts demonstrated that interactions between different classes of pigment cells are essential for normal stripes to develop, though the genes and cell behaviors involved have yet to be elucidated. In proposed Aim 1, time-lapse imaging will be used to visualize cell-cell interactions during stripe development and regeneration, and to test the hypothesis that direct, short-range and long- range contacts are involved. Aim 2 will test functions of previously isolated and new genes for which mutants have boundary-defective phenotypes. In addition to normal development, these studies will extent to imaging the behavior of melanoma cells and how invasion and metastasis by these cells is affected by genetic background. Aim 3 will build upon earlier studies by testing a new class of pigment cell for its function in boundary formation, as well as the role of a candidate genetic pathway for mediating these effects. Finally, Aim 4 will identify new genes and pathways contributing to stripe boundary formation through the analysis of candidate pathways as well as comparisons of whole transcriptomes between defined pigment cell populations across stages and genetic backgrounds. These studies will provide valuable new insights into the genetics of pigment cell boundary formation and melanoma progression, as well as the logic of boundary forming mechanisms more generally.